One of conventional fuel cell stacks is described in Patent Document 1, which is titled sealing structure of fuel cell. The fuel cell stack in Patent Document 1 includes a plurality of cells stacked. Each of the cells includes a cell plate, an anode current collector, a cell frame and a separator. In a pair of cells adjacent in the stacking direction of the fuel cell stack, the cell frame of one cell of the pair of cells has a sealing groove while the separator of the other cell of the pair of cells has a protrusion corresponding to the sealing groove. In the fuel cell stack, a sealing member for sealing a gas channel is disposed between the sealing groove and the protrusion. The sealing member softens in the range of operation temperature of the fuel cell.